A stent is commonly used as a tubular structure left inside the lumen of a duct to relieve an obstruction. Commonly, stents are inserted into the lumen in a non expanded form and are then expanded autonomously (Tihon et al. (1994) U.S. Pat. No. 5,356,423) or with the aid of a second device in situ. Although a number of designs have been reported, these designs have suffered from a number of limitations. These include; restrictions on the dimension of the stent (Cardon et al. 1995 U.S. Pat. No 5,383,892). Cardon et al. describes a stent that has rigid ends (8 mm) and a flexible median part of 7-21 mm. This device is formed of multiple parts and is not continuously flexible along the longitudinal axis. Another stent design that has rigid segments and flexible segments has been described by Pinchasik et al. U.S. Pat. No. 5,449,373 (1995).
Other stents are described as longitudinally flexible (Lau et al.(1995) U.S. Pat. No. 5,421,955 also EP application 540290 A2, A3) but consist of a plurality of cylindrical elements connected by flexible members. This design has at least one important disadvantage, for example, according to this design, protruding edges occur when the stent is flexed around a curve raising the possibility of inadvertent retention of the stent on plaque deposited on arterial walls. This may cause the stent to embolize or move out of position and further cause damage to the interior lining of healthy vessels. (see FIG. 1(a) below).
Thus, stents known in the art, which may be expanded by balloon angioplasty, generally compromise axial flexibility to permit expansion and provide overall structural integrity.